U.S. patent application number 14/416368 was filed with the patent office on 2015-06-25 for mobile station, small radio base station, and communication control method.
This patent application is currently assigned to NTT DOCOMO, INC.. The applicant listed for this patent is NTT DOCOMO, INC.. Invention is credited to Hiroyuki Ishii, Tooru Uchino.
Application Number | 20150181508 14/416368 |
Document ID | / |
Family ID | 49997167 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150181508 |
Kind Code |
A1 |
Uchino; Tooru ; et
al. |
June 25, 2015 |
MOBILE STATION, SMALL RADIO BASE STATION, AND COMMUNICATION CONTROL
METHOD
Abstract
A "macro-assisted cell" adaptable to multiple operation modes is
realized. In a mobile station (UE) of the invention, a control unit
(22) is configured to start communication in a small cell on the
basis of MIB/SIB of the small cell when a sequence in a "discovery
signal" is determined as a sequence for a "stand-alone cell." The
control unit (22) is configured to start the communication in the
small cell on the basis of a control signal from a macro cell when
the sequence in the "discovery signal" is determined as a sequence
for a "macro-assisted cell."
Inventors: |
Uchino; Tooru; (Tokyo,
JP) ; Ishii; Hiroyuki; (Palo Alto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NTT DOCOMO, INC. |
Tokyo |
|
JP |
|
|
Assignee: |
NTT DOCOMO, INC.
Tokyo
JP
|
Family ID: |
49997167 |
Appl. No.: |
14/416368 |
Filed: |
July 17, 2013 |
PCT Filed: |
July 17, 2013 |
PCT NO: |
PCT/JP2013/069409 |
371 Date: |
January 22, 2015 |
Current U.S.
Class: |
455/434 |
Current CPC
Class: |
H04W 16/32 20130101;
H04W 48/16 20130101 |
International
Class: |
H04W 48/16 20060101
H04W048/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 2012 |
JP |
2012-167507 |
Claims
1. A mobile station used in a mobile communication system provided
with a macro cell and a small cell, where the small cell is any of
a first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station comprising: a reception unit
configured to detect a prescribed signal transmitted by the small
cell; and a control unit configured to determine whether a sequence
in the prescribed signal is a sequence for the first cell or a
sequence for the second cell, wherein when the sequence in the
prescribed signal is determined as the sequence for the first cell,
the control unit is configured to start communication in the small
cell on the basis of broadcast information of the small cell, and
when the sequence in the prescribed signal is determined as the
sequence for the second cell, the control unit is configured to
start the communication in the small cell on the basis of a control
signal from the macro cell.
2. A mobile station used in a mobile communication system provided
with a macro cell and a small cell, where the small cell is any of
a first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station comprising: a reception unit
configured to detect a synchronization signal transmitted by the
small cell; and a control unit configured to determine whether a
sequence in the synchronization signal is a sequence for the first
cell or a sequence for the second cell, wherein when the sequence
in the synchronization signal is determined as the sequence for the
first cell, the control unit is configured to start communication
in the small cell on the basis of broadcast information of the
small cell, and when the sequence in the synchronization signal is
determined as the sequence for the second cell, the control unit is
configured to start the communication in the small cell on the
basis of a control signal from the macro cell.
3. A mobile station used in a mobile communication system provided
with a macro cell and a small cell, where the small cell is any of
a first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station comprising: a reception unit
configured to detect a synchronization signal transmitted by the
small cell, and then to receive a prescribed signal transmitted by
using a subframe which is the same as or located at the periphery
of a subframe of the synchronization signal; and a control unit
configured to determine whether the small cell is the first cell or
the second cell on the basis of a content of notification by the
prescribed signal, wherein when the small cell is determined as the
first cell, the control unit is configured to start communication
in the small cell on the basis of broadcast information of the
small cell, and when the small cell is determined as the second
cell, the control unit is configured to start the communication in
the small cell on the basis of a control signal from the macro
cell.
4. A mobile station used in a mobile communication system provided
with a macro cell and a small cell, where the small cell is any of
a first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station comprising: a reception unit
configured to detect a synchronization signal transmitted by the
small cell, and then to receive a prescribed signal; and a control
unit configured to determine whether a sequence in the prescribed
signal is a sequence for the first cell or a sequence for the
second cell, wherein when the sequence in the prescribed signal is
determined as the sequence for the first cell, the control unit is
configured to start communication in the small cell on the basis of
broadcast information of the small cell, and when the sequence in
the prescribed signal is determined as the sequence for the second
cell, the control unit is configured to start the communication in
the small cell on the basis of a control signal from the macro
cell.
5. A mobile station used in a mobile communication system provided
with a macro cell and a small cell, where the small cell is any of
a first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station comprising: a reception unit
configured to receive broadcast information transmitted by the
small cell; and a control unit configured to determine whether the
small cell is the first cell or the second cell on the basis of a
content of notification by the broadcast information, wherein when
the small cell is determined as the first cell, the control unit is
configured to start communication in the small cell on the basis of
the rest of the broadcast information of the small cell, and when
the small cell is determined as the second cell, the control unit
is configured to start the communication in the small cell on the
basis of a control signal from the macro cell.
6. A mobile station used in a mobile communication system provided
with a macro cell and a small cell, where the small cell is any of
a first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station comprising: a control unit
configured to determine whether or not specific broadcast
information of the macro cell notifies that a carrier for cell
reselection is a carrier on which only the first cell is present,
wherein when the control unit determines that the specific
broadcast information notifies that the carrier for the cell
reselection is the carrier on which only the first cell is present,
the control unit is configured to perform the cell reselection of
the cell on the carrier, and then to start communication in the
cell on the basis of broadcast information of the cell, and when
the control unit determines that the specific broadcast information
does not notify that the carrier for the cell reselection is the
carrier on which only the first cell is present, the control unit
is configured to start the communication with the cell on the
carrier on the basis of a control signal from the macro cell.
7. A small radio base station configured to manage a small cell,
where the small cell is any of a first cell capable of being
operated independently of a macro cell under control of a macro
radio base station and a second cell incapable of being operated
independently of the macro cell, the small radio base station
comprising: a transmission unit configured to transmit a prescribed
signal, wherein the transmission unit is configured to use a
sequence for the first cell as a sequence in the prescribed signal
when the small cell is operated as the first cell, and to use a
sequence for the second cell as the sequence in the prescribed
signal when the small cell is operated as the second cell.
8. A communication control method for a mobile station usable in a
mobile communication system provided with a macro cell and a small
cell, where the small cell is any of a first cell capable of being
operated independently of the macro cell and a second cell
incapable of being operated independently of the macro cell, the
method comprising: a first step of detecting a prescribed signal
transmitted by the small cell; a second step of determining whether
a sequence in the prescribed signal is a sequence for the first
cell or a sequence for the second cell; and a third step of
starting communication in the small cell, wherein when the sequence
in the prescribed signal is determined as the sequence for the
first cell in the second step, the communication in the small cell
is started in the third step on the basis of broadcast information
of the small cell, and when the sequence in the prescribed signal
is determined as the sequence for the second cell in the second
step, the communication in the small cell is started in the third
step on the basis of a control signal from the macro cell.
9. A small radio base station configured to manage a small cell,
where the small cell is any of a first cell capable of being
operated independently of a macro cell under control of a macro
radio base station and a second cell incapable of being operated
independently of the macro cell, wherein the small radio base
station switches the small cell so as to be operated as any one of
the first cell and the second cell depending on an operation status
of the macro cell.
Description
TECHNICAL FIELD
[0001] The present invention relates to a mobile station, a small
radio base station, and a communication control method.
BACKGROUND ART
[0002] In June 2012, 3GPP hosted a workshop that involved radio
access techniques in the future.
[0003] In the workshop, many companies proposed an "enhanced small
cell" as one of the radio access techniques in the future (see
Non-patent document 1).
[0004] Particularly, a "macro-assisted cell (or a phantom cell)"
was proposed in addition to the existing "stand-alone cell" (see
Non-patent document 2).
[0005] The followings are characteristics of a mobile communication
system in which the "macro-assisted cell" is located.
[0006] The mobile communication system is configured to split
C-plane and U-plane between a macro cell and the "macro-assisted
cell."
[0007] As a result, the macro cell can maintain excellent mobility
and connectivity by supporting the C-plane (RRC signaling) at a low
frequency used in a conventional mobile communication system.
[0008] In the meantime, the "macro-assisted cell" can provide
communication with fast throughput as well as flexible and
efficient cost and power by performing the communication of the
U-plane (user data) while using a high frequency where a broadband
is available.
[0009] Here, unlike the existing cell, the "macro-assisted cell" is
not required to transmit a reference signal common to cells, a
synchronization signal, or broadcast information (MIB/SIB). In this
regard, the "macro-assisted cell" is a cell with a different
concept from that of the conventional cell.
[0010] Meanwhile, in the mobile communication system in which the
"macro-assisted cell" is located, the C-plane and the U-plane are
generally split between the macro cell and the "macro-assisted
cell" as described above. Specifically, the macro cell transmits
the C-plane while the "macro-assisted cell" transmits the U-plane.
Such assignments of the C-plane and the U-plane may be strict or
not.
[0011] For example, part of the U-plane may be transmitted by the
macro cell. To be more precise, since connectivity or stability is
important in a "real time service" such as a voice service, the
macro cell may transmit such a "real time service" also in
consideration of quality during high-speed movement.
[0012] On the other hand, concerning the C-plane as well, control
information that is important in establishing the communication may
be transmitted by the macro cell while other less important control
information may be transmitted by the "macro-assisted cell."
[0013] In the above-described mobile communication system, a mobile
station UE can establish connection to both of the macro cell and
the "macro-assisted cell" at the same time.
[0014] Note that the "macro-assisted cell" is a cell which can be
operated only within the coverage of the macro cell.
PRIOR ART DOCUMENTS
Non-Patent Documents
[0015] Non-patent document 1: RWS-120045,
http://3gpp.org/Future-Radio-in-3GPP-300-attend (searched on Jul.
25, 2012)
[0016] Non-patent document 2: RWS-120010,
http://3gpp.org/Future-Radio-in-3GPP-300-attend (searched on Jul.
25, 2012)
SUMMARY OF THE INVENTION
[0017] As described above, in order to operate the "macro-assisted
cell," there is a restriction that the "macro-assisted cell" has to
be located within the coverage of the macro cell.
[0018] However, some areas or certain places, such as regions in
the back of indoor or underground places, may often be out of the
coverage of the macro cell.
[0019] In such areas or places, it is preferable that the
"macro-assisted cell" be operated as the "stand-alone cell" as in
the conventional example.
[0020] Meanwhile, from the perspective of "manufacturing" or of the
standard specifications, it is desirable that the "macro-assisted
cell" and the "stand-alone cell" have a mutual radio interface as
much as possible.
[0021] In the meantime, it is desirable that the "macro-assisted
cell" remain capable of being operated as the "stand-alone cell" if
the macro cell stops a radio communication service for some reason
(such as a failure).
[0022] The present invention has been made in view of the
aforementioned problems. An objective of the present invention is
to provide a mobile station, a small radio base station, and a
communication control method, which are capable of realizing a
"macro-assisted cell" adaptable to multiple operation modes.
[0023] A first feature of the present invention is summarized as a
mobile station used in a mobile communication system provided with
a macro cell and a small cell, where the small cell is any of a
first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station including: a reception unit
configured to detect a prescribed signal transmitted by the small
cell; and a control unit configured to determine whether a sequence
in the prescribed signal is a sequence for the first cell or a
sequence for the second cell. Here, when the sequence in the
prescribed signal is determined as the sequence for the first cell,
the control unit is configured to start communication in the small
cell on the basis of broadcast information of the small cell, and
when the sequence in the prescribed signal is determined as the
sequence for the second cell, the control unit is configured to
start the communication in the small cell on the basis of a control
signal from the macro cell.
[0024] A second feature of the present invention is summarized as a
mobile station used in a mobile communication system provided with
a macro cell and a small cell, where the small cell is any of a
first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station including: a reception unit
configured to detect a synchronization signal transmitted by the
small cell; and a control unit configured to determine whether a
sequence in the synchronization signal is a sequence for the first
cell or a sequence for the second cell. Here, when the sequence in
the synchronization signal is determined as the sequence for the
first cell, the control unit is configured to start communication
in the small cell on the basis of broadcast information of the
small cell, and when the sequence in the synchronization signal is
determined as the sequence for the second cell, the control unit is
configured to start the communication in the small cell on the
basis of a control signal from the macro cell.
[0025] A third feature of the present invention is summarized as a
mobile station used in a mobile communication system provided with
a macro cell and a small cell, where the small cell is any of a
first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station including: a reception unit
configured to detect a synchronization signal transmitted by the
small cell, and then to receive a prescribed signal transmitted by
using a subframe which is the same as or located at the periphery
of a subframe of the synchronization signal; and a control unit
configured to determine whether the small cell is the first cell or
the second cell on the basis of a content of notification by the
prescribed signal. Here, when the small cell is determined as the
first cell, the control unit is configured to start communication
in the small cell on the basis of broadcast information of the
small cell, and when the small cell is determined as the second
cell, the control unit is configured to start the communication in
the small cell on the basis of a control signal from the macro
cell.
[0026] A fourth feature of the present invention is summarized as a
mobile station used in a mobile communication system provided with
a macro cell and a small cell, where the small cell is any of a
first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station including: a reception unit
configured to detect a synchronization signal transmitted by the
small cell, and then to receive a prescribed signal; and a control
unit configured to determine whether a sequence in the prescribed
signal is a sequence for the first cell or a sequence for the
second cell. Here, when the sequence in the prescribed signal is
determined as the sequence for the first cell, the control unit is
configured to start communication in the small cell on the basis of
broadcast information of the small cell, and when the sequence in
the prescribed signal is determined as the sequence for the second
cell, the control unit is configured to start the communication in
the small cell on the basis of a control signal from the macro
cell.
[0027] A fifth feature of the present invention is summarized as a
mobile station used in a mobile communication system provided with
a macro cell and a small cell, where the small cell is any of a
first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station including: a reception unit
configured to receive broadcast information transmitted by the
small cell; and a control unit configured to determine whether the
small cell is the first cell or the second cell on the basis of a
content of notification by the broadcast information. Here, when
the small cell is determined as the first cell, the control unit is
configured to start communication in the small cell on the basis of
the rest of the broadcast information of the small cell, and when
the small cell is determined as the second cell, the control unit
is configured to start the communication in the small cell on the
basis of a control signal from the macro cell.
[0028] A sixth feature of the present invention is summarized as a
mobile station used in a mobile communication system provided with
a macro cell and a small cell, where the small cell is any of a
first cell capable of being operated independently of the macro
cell and a second cell incapable of being operated independently of
the macro cell, the mobile station including: a control unit
configured to determine whether or not specific broadcast
information of the macro cell notifies that a carrier for cell
reselection is a carrier on which only the first cell is present.
Here, when the control unit determines that the specific broadcast
information notifies that the carrier for the cell reselection is
the carrier on which only the first cell is present, the control
unit is configured to perform the cell reselection of the cell on
the carrier, and then to start communication in the cell on the
basis of broadcast information of the cell, and when the control
unit determines that the specific broadcast information does not
notify that the carrier for the cell reselection is the carrier on
which only the first cell is present, the control unit is
configured to start the communication with the cell on the carrier
on the basis of a control signal from the macro cell.
[0029] A seventh feature of the present invention is summarized as
a small radio base station configured to manage a small cell, where
the small cell is any of a first cell capable of being operated
independently of a macro cell under control of a macro radio base
station and a second cell incapable of being operated independently
of the macro cell, the small radio base station including: a
transmission unit configured to transmit a prescribed signal. Here,
the transmission unit is configured to use a sequence for the first
cell as a sequence in the prescribed signal when the small cell is
operated as the first cell, and to use a sequence for the second
cell as the sequence in the prescribed signal when the small cell
is operated as the second cell.
[0030] A eighth feature of the present invention is summarized as a
communication control method for a mobile station usable in a
mobile communication system provided with a macro cell and a small
cell, where the small cell is any of a first cell capable of being
operated independently of the macro cell and a second cell
incapable of being operated independently of the macro cell, the
method including: a first step of detecting a prescribed signal
transmitted by the small cell; a second step of determining whether
a sequence in the prescribed signal is a sequence for the first
cell or a sequence for the second cell; and a third step of
starting communication in the small cell. Here, when the sequence
in the prescribed signal is determined as the sequence for the
first cell in the second step, the communication in the small cell
is started in the third step on the basis of broadcast information
of the small cell, and when the sequence in the prescribed signal
is determined as the sequence for the second cell in the second
step, the communication in the small cell is started in the third
step on the basis of a control signal from the macro cell.
[0031] A ninth feature of the present invention is summarized as a
small radio base station configured to manage a small cell, where
the small cell is any of a first cell capable of being operated
independently of a macro cell under control of a macro radio base
station and a second cell incapable of being operated independently
of the macro cell, wherein the small radio base station switches
the small cell so as to be operated as any one of the first cell
and the second cell depending on an operation status of the macro
cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is an overall configuration diagram of a mobile
communication system according to a first embodiment of the present
invention.
[0033] FIG. 2 is a functional block diagram of a small radio base
station according to the first embodiment of the present
invention.
[0034] FIG. 3 is a view showing examples of synchronization signals
to be transmitted by the small radio base station according to the
first embodiment of the present invention.
[0035] FIG. 4 is a view showing an example of a "discovery signal"
to be transmitted by the small radio base station according to the
first embodiment of the present invention.
[0036] FIG. 5 is a functional block diagram of a macro radio base
station and a mobile station according to the first embodiment of
the present invention.
[0037] FIG. 6 is a flowchart showing an operation of the mobile
station according to the first embodiment of the present
invention.
[0038] FIG. 7 is a view showing examples of synchronization signals
to be transmitted by a small radio base station according to a
first modified example of the present invention.
[0039] FIG. 8 is a flowchart showing an operation of a mobile
station according to the first modified example of the present
invention.
[0040] FIG. 9 is a view showing an example of a new signal to be
transmitted by a small radio base station according to a second
modified example of the present invention.
[0041] FIG. 10 is a flowchart showing an operation of a mobile
station according to the second modified example of the present
invention.
[0042] FIG. 11 is a flowchart showing an operation of a mobile
station according to a third modified example of the present
invention.
[0043] FIG. 12 is a view showing an example of broadcast
information to be transmitted by a small radio base station
according to a fourth modified example of the present
invention.
[0044] FIG. 13 is a view showing the example of the broadcast
information to be transmitted by the small radio base station
according to the fourth modified example of the present
invention.
[0045] FIG. 14 is a flowchart showing an operation of a mobile
station according to the fourth modified example of the present
invention.
[0046] FIG. 15 is a view showing an example of broadcast
information to be transmitted by a small radio base station
according to a fifth modified example of the present invention.
[0047] FIG. 16 is a flowchart showing an operation of a mobile
station according to the fifth modified example of the present
invention.
[0048] FIG. 17 is a flowchart showing an operation of a small radio
base station according to a sixth modified example of the present
invention.
MODES FOR CARRYING OUT THE INVENTION
Mobile Communication System According to First Embodiment of
Present Invention
[0049] A mobile communication system according to a first
embodiment of the present invention will be described with
reference to FIG. 1 to FIG. 6.
[0050] An LTE mobile communication system is described as an
example in this embodiment. However, the present invention is not
limited only to such a mobile communication system, but are also
applicable to mobile communication systems of other schemes.
[0051] As shown in FIG. 1, a cell #1 being a "macro cell" as well
as a cell #110A, a cell #110B, a cell #110C, a cell #110D, a cell
#110E, and so forth each being a "small cell," are located in the
mobile communication of this embodiment.
[0052] Here, in the macro cell, a macro radio base station Macro
eNB provides mobile communication services. Meanwhile, in each
small cell, a small radio base station Small eNB #11 (Small eNB
#11A, Small eNB #11B, Small eNB #11C, Small eNB #11D or Small eNB
#11E in the example of FIG. 1) provides mobile communication
services. Specifically, the small radio base stations Small eNB
#11A, Small eNB #11B, Small eNB #11C, Small eNB #11D, and Small eNB
#11E provide the mobile communication services in the cell #110A,
the cell #110B, the cell #110C, the cell #110D, and the cell #110E,
respectively.
[0053] In the example of FIG. 1, the cell #1 is operated in the 2
GHz band while the cell #110A, the cell #110B, and the cell #110C
are operated in the 3.5 GHz band.
[0054] Note that the frequency bands such as the 2 GHz band and the
3.5 GHz band are mere examples. A frequency band other than the 2
GHz band may be used by the cell #1 while a frequency band other
than the 3.5 GHz band may be used by the cell #110A, the cell
#110B, the cell #110C, the cell #110D, and/or the cell #110E.
[0055] For example, the cell #110A may be a "macro-assisted cell (a
phantom cell)" while the cell #110B may be a "stand-alone
cell."
[0056] When the cell #110A is the "macro-assisted cell," a mobile
station UE is configured to establish connection to both of the
macro radio base station Macro eNB and the small radio base station
Small eNB #11A, to perform transmission and reception of C-plane to
and from the macro radio base station Macro eNB, and to perform
transmission and reception of U-plane to and from the small radio
base station Small eNB #11A.
[0057] To be more precise, the connection between the mobile
station UE and the small radio base station Small eNB #11A is
established on the basis of a control signal (the C-plane)
exchanged between the mobile station UE and the macro radio base
station Macro eNB, and the mobile station UE exchanges user data
(the U-plane) with the small radio base station Small eNB #11A by
using the connection between the mobile station UE and the small
radio base station Small eNB #11A thus established.
[0058] As shown in FIG. 2, each small radio base station Small eNB
includes a transmission unit 111 and a reception unit 112. The
small radio base stations Small eNB #11A, Small eNB #11B, Small eNB
#11C, Small eNB #11D, and Small eNB #11E have the same
configuration, functions, and conditions. Accordingly, in the
following descriptions, these small radio base stations will be
collectively referred to as the small radio base station Small eNB
unless otherwise stated. It is to be also noted that the cell under
control of the small radio base station Small eNB will be called
the cell #110.
[0059] The transmission unit 111 is configured to transmit various
signals to the mobile station UE in the cell #110 under control of
the small radio base station Small eNB. The reception unit 112 is
configured to receive various signals from the mobile station UE in
the cell #110 under control of the small radio base station Small
eNB.
[0060] For example, the transmission unit 111 is configured to
transmit a PSS (primary synchronization signal) and an SSS
(secondary synchronization signal) in the cell #110 under control
of the small radio base station Small eNB.
[0061] Each cell has 504 PCIs (physical cell IDs). In the meantime,
each of the PSS and the SSS has a sequence of 504 pieces, so that
the mobile station UE can specify a PCI by specifying a sequence in
any of the PSS and the SSS.
[0062] As shown in FIG. 3, the PSS and the SSS are defined to be
located at the end of first slots of subframes 0 and 5 in a radio
frame, respectively.
[0063] The PSS and the SSS are defined to be located at a cycle of
5 ms in consideration of an overhead, a time diversity effect, LTE
cell selection and cell reselection as well as a measurement by a
different system, and so forth.
[0064] Meanwhile, as shown in FIG. 4, the transmission unit 111 is
configured to transmit a "discovery signal", which is a newly
defined signal, in addition to the PSS and the SSS.
[0065] Here, part of a sequence in the "discovery signal" will be
defined as a sequence for the "stand-alone cell" while the rest of
the sequence in the "discovery signal" will be defined as a
sequence for the "macro-assisted cell."
[0066] For example, a sequence in the "discovery signal" having IDs
from "0" to "503" may be defined as the sequence for the
"stand-alone cell" while a sequence in the "discovery signal"
having IDs from "504" to "1007" may be defined as the sequence for
the "macro-assisted cell."
[0067] Here, by defining the position of the "discovery signal" in
the form of specifications such as "SFN (system frame number) #N1,
subframe number #N2, and resource block numbers #N3 and #N4," the
mobile station LIE can detect positions of the PSS and the SSS just
by detecting the "discovery signal."
[0068] In the description made above, the "#N1" is the number that
specifies the system frame number, the "#N2" is the number that
specifies the subframe number, and the "#N3" and "#N4" are the
numbers that specify the resource block numbers.
[0069] Meanwhile, in addition to the determination as to whether or
not a certain cell is the "macro-assisted cell" depending on the
sequence in the "discovery signal," the determination as to whether
or not the certain cell is the "macro-assisted cell" may be made
depending on a resource position (in terms of time or the
frequency) of the "discovery signal."
[0070] As shown in FIG. 5(a), the mobile station UE includes a
reception unit 21, a control unit 22, and a transmission unit
23.
[0071] The reception unit 21 is configured to receive various
signals from the macro radio base station Macro eNB that manages
the cell #1 and from the small radio base station Small eNB that
manages the cell #110. The transmission unit 23 is configured to
transmit various signals to the macro radio base station Macro eNB
that manages the cell #1 and to the small radio base station Small
eNB that manages the cell #110.
[0072] Here, concerning the small cell, i.e., in the 3.5 GHz band,
the reception unit 21 is configured to detect the above-described
"discovery signal" in addition to the PSS and the SSS.
[0073] The control unit 22 is configured to determine whether a
sequence in the "discovery signal" is a sequence for the
"stand-alone cell" or a sequence for the "macro-assisted cell."
[0074] Here, when the sequence in the "discovery signal" is
determined as the sequence for the "stand-alone cell," the control
unit 22 is configured to start communication in the small cell on
the basis of the MIB/SIB of the small cell. In other words, the
control unit 22 is configured to establish connection (the U-plane
and the C-plane) in the "stand-alone cell."
[0075] On the other hand, when the sequence in the "discovery
signal" is determined as the sequence for the "macro-assisted
cell," the control unit 22 is configured to start the communication
in the small cell on the basis of the control signal from the macro
cell. In other words, the control unit 22 is configured to
establish the connection in the small cell on the basis of the
control signal (the C-plane) exchanged between the macro radio base
station Macro eNB and the mobile station UE.
[0076] In this case, the reception unit 21 is configured not to
receive the broadcast information of the small cell (the
"macro-assisted cell").
[0077] Meanwhile, the reception unit 21 is configured to acquire
control signals (which correspond to the MIB/SIB) for the
above-described small cell (the "macro-assisted cell") through an
individual control signal and broadcast information from the macro
radio base station Macro eNB.
[0078] As shown in FIG. 5 (b), the macro radio base station Macro
eNB includes a transmission unit 31 and a reception unit 32.
[0079] The transmission unit 31 is configured to transmit various
signals to the mobile station UE in the macro cell under control of
the macro radio base station Macro eNB. The reception unit 32 is
configured to receive various signals from the mobile station UE in
the macro cell under control of the macro radio base station Macro
eNB.
[0080] Moreover, the transmission unit 31 transmits the control
signals (which correspond to the MIB/SIB) for the small cell (the
"macro-assisted cell") using the individual control signal and the
broadcast information.
[0081] Furthermore, when the mobile station UE establishes the
connection to the small radio base station Small eNB in the small
cell (the "macro-assisted cell"), the transmission unit 31
transmits a control signal, which is for establishing the
above-mentioned connection, to the mobile station UE by using
individual control signal.
[0082] The individual control signal may be notified by use of an
RRC layer, or any other layers including a PDCP layer, an RLC
layer, a MAC layer, a physical layer, and the like.
[0083] An operation of the mobile station UE of this embodiment
will be described below with reference to FIG. 6.
[0084] As shown in FIG. 6, when the mobile station UE detects the
"discovery signal" in the small cell in step S101, the mobile
station UE determines whether the sequence in the "discovery
signal" is the sequence for the "stand-alone cell" or the sequence
for the "macro-assisted cell" in step S102.
[0085] When the sequence in the "discovery signal" is determined as
the sequence for the "stand-alone cell," the mobile station UE
receives the MIB and the SIB of the small cell in step S103.
[0086] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection by the same method as the one used in the case of an
ordinary (conventional) "stand-alone cell."
[0087] On the other hand, when the sequence in the "discovery
signal" is determined as the sequence for the "macro-assisted
cell," the mobile station UE receives the control signals
corresponding to the MIB and the SIB of the small cell in step S104
through the individual control signal, the broadcast information,
and the like from the macro radio base station Macro eNB.
[0088] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection on the basis of the individual control signal from the
macro radio base station Macro eNB.
[0089] The individual control signal may be notified by use of the
RRC layer, or any other layers including the PDCP layer, the RLC
layer, the MAC layer, the physical layer, and the like.
[0090] According to the mobile communication system of this
embodiment, the mobile station UE can determine whether the small
cell is the "stand-alone cell" or the "macro-assisted cell" on the
basis of the detected sequence in the "discovery signal."
[0091] As a consequence, a particular small cell can be operated
both as the "stand-alone cell" and as the "macro-assisted cell" by
changing the sequence in the "discovery signal" transmitted in the
small cell.
First Modified Example
[0092] A mobile communication system according to a first modified
example of the present invention will be described with reference
to FIG. 7 and FIG. 8, while focusing on differences from the
above-described mobile communication system according to the first
embodiment.
[0093] In the mobile communication system according to the first
modified example, part of a sequence in the PSS/SSS is defined as
the sequence for the "stand-alone cell" while the rest of the
sequence is defined as the sequence for the "macro-assisted
cell."
[0094] For example, a sequence in the PSS/SSS having IDs from "0"
to "99" may be defined as the sequence for the "stand-alone cell"
while a sequence in the PSS/SSS having IDs from "100" to "503" may
be defined as the sequence for the "macro-assisted cell."
[0095] Meanwhile, the transmission unit 111 in the small radio base
station Small eNB is configured to transmit the PSS and the SSS as
shown in FIG. 7.
[0096] The control unit 22 in the mobile station UE is configured
to determine whether a certain sequence in the PSS/SSS in the small
cell is a sequence for the "stand-alone cell" or a sequence for the
"macro-assisted cell."
[0097] Here, when the sequence in the PSS/SSS in the small cell is
determined as the sequence for the "stand-alone cell," the control
unit 22 is configured to start the communication in the small cell
on the basis of the MIB/SIB of the small cell. In other words, the
control unit 22 is configured to establish the connection (the
U-plane and the C-plane) in the "stand-alone cell."
[0098] On the other hand, when the sequence in the PSS/SSS in the
small cell is determined as the sequence for the "macro-assisted
cell," the control unit 22 is configured to start the communication
in the small cell on the basis of the control signal from the macro
cell. In other words, the control unit 22 is configured to
establish the connection in the small cell on the basis of the
control signal (the C-plane) exchanged between the macro radio base
station Macro eNB and the mobile station UE.
[0099] An operation of the mobile station UE of the first modified
example will be described below with reference to FIG. 8.
[0100] As shown in FIG. 8, when the mobile station UE detects the
PSS/SSS in the small cell in step S201, the mobile station UE
determines whether the sequence in the PSS/SSS is the sequence for
the "stand-alone cell" or the sequence for the "macro-assisted
cell" in step S202.
[0101] When the sequence in the PSS/SSS is determined as the
sequence for the "stand-alone cell," the mobile station UE receives
the MIB and the SIB of the small cell in step S203.
[0102] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection by the same method as the one used in the case of the
ordinary (conventional) "stand-alone cell."
[0103] On the other hand, when the sequence in the PSS/SSS is
determined as the sequence for the "macro-assisted cell," the
mobile station UE receives the control signals corresponding to the
MIB and the SIB of the small cell in step S204 through the
individual control signal, the broadcast information, and the like
from the macro radio base station Macro eNB.
[0104] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection on the basis of the individual control signal from the
macro radio base station Macro eNB.
[0105] According to the mobile communication system of the first
modified example, the mobile station UE can determine whether the
small cell is the "stand-alone cell" or the "macro-assisted cell"
on the basis of the detected sequence in the PSS/SSS.
[0106] As a consequence, a particular small cell can be operated
both as the "stand-alone cell" and as the "macro-assisted cell" by
changing the sequence in the PSS/SSS transmitted in the small
cell.
Second Modified Example
[0107] A mobile communication system according to a second modified
example of the present invention will be described with reference
to FIG. 9 and FIG. 10, while focusing on differences from the
above-described mobile communication system according to the first
embodiment.
[0108] As shown in FIG. 9, in the mobile communication system
according to the second modified example, the transmission unit ill
in the small radio base station Small eNB is configured to transmit
a new signal by using a subframe which is either the same as or
located at the periphery of a subframe of the PSS/SSS.
[0109] Here, the new signal is a signal which notifies whether the
cell transmitting the new signal is the "stand-alone cell" or the
"macro-assisted cell."
[0110] The new signal may be a signal which uses one bit just for
identifying the "stand-alone cell" or the "macro-assisted cell" or
may be a signal corresponding to the above-described "discovery
signal."
[0111] After the detection of the PSS/SSS transmitted in the small
cell, the reception unit 21 in the mobile station UE is configured
to receive the new signal transmitted by using the subframe which
is the same as or located at the periphery of the subframe of the
PSS/SSS.
[0112] The control unit 22 in the mobile station UE is configured
to determine whether the small cell is the "stand-alone cell" or
the "macro-assisted cell" on the basis of the content of
notification by the new signal.
[0113] Alternatively, the control unit 22 in the mobile station UE
may be configured to determine whether the small cell is the
"stand-alone cell" or the "macro-assisted cell" depending on a
resource position (in terms of time or the frequency) of the
above-described new signal.
[0114] Here, when the small cell is determined as the "stand-alone
cell," the control unit 22 is configured to start the communication
in the small cell on the basis of the MIB/SIB of the small cell. In
other words, the control unit 22 is configured to establish the
connection (the U-plane and the C-plane) in the "stand-alone
cell."
[0115] On the other hand, when the small cell is determined as the
"macro-assisted cell," the control unit 22 is configured to start
the communication in the small cell on the basis of the control
signal from the macro cell. In other words, the control unit 22 is
configured to establish the connection in the small cell on the
basis of control signal (the C-plane) exchanged between the macro
radio base station Macro eNB and the mobile station UE.
[0116] The individual control signal may be notified by use of the
RRC layer, or any other layers including the PDCP layer, the RLC
layer, the MAC layer, the physical layer, and the like.
[0117] Meanwhile, when the new signal is the signal corresponding
the above-described "discovery signal," the control unit 22 may be
configured to detect an ID (such as a phantom cell ID) of the small
cell.
[0118] In the meantime, the new signal need not be the signal used
for detecting the cell, such as the "discovery signal" of the first
embodiment and the PSS/SSS described above.
[0119] An operation of the mobile station UE of the second modified
example will be described below with reference to FIG. 10.
[0120] As shown in FIG. 10, when the mobile station UE detects the
PSS/SSS in the small cell in step S301, the mobile station UE
receives the new signal and determines whether the small cell is
the "stand-alone cell" or the "macro-assisted cell" in step S302 on
the basis of the content of notification by the new signal.
[0121] When the small cell is determined as the "stand-alone cell,"
the mobile station UE receives the MIB and the SIB of the small
cell in step S303.
[0122] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection by the same method as the one used in the case of the
ordinary (conventional) "stand-alone cell."
[0123] On the other hand, when the small cell is determined as the
"macro-assisted cell," the mobile station UE receives the control
signals corresponding to the MIB and the SIB of the small cell in
step S304 through the individual control signal, the broadcast
information, and the like from the macro radio base station Macro
eNB.
[0124] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection on the basis of the individual control signal from the
macro radio base station Macro eNB.
[0125] According to the mobile communication system of the second
modified example, the mobile station UE can determine whether the
small cell is the "stand-alone cell" or the "macro-assisted cell"
on the basis of the received new signal.
[0126] As a consequence, a particular small cell can be operated
both as the "stand-alone cell" and as the "macro-assisted cell" by
changing the content of notification by the new signal transmitted
in the small cell.
Third Modified Example
[0127] A mobile communication system according to a third modified
example of the present invention will be described with reference
to FIG. 11, while focusing on differences from the above-described
mobile communication system according to the first embodiment.
[0128] In the mobile communication system according to the third
modified example, the reception unit 21 in the mobile station UE is
configured to receive the "discovery signal" after the detection of
the PSS/SSS transmitted in the small cell.
[0129] Here, the reception unit 21 is configured to detect the cell
by using the PSS/SSS instead of detecting the cell by using the
"discovery signal."
[0130] An operation of the mobile station UE of the third modified
example will be described below with reference to FIG. 11.
[0131] As shown in FIG. 11, in step S401, the mobile station UE
receives the "discovery signal" after detecting the PSS/SSS in the
small cell. In step S402, the mobile station UE determines whether
the sequence in the "discovery signal" is the sequence for the
"stand-alone cell" or the sequence for the "macro-assisted
cell."
[0132] When the sequence in the "discovery signal" is determined as
the sequence for the "stand-alone cell," the mobile station UE
receives the MIB and the SIB of the small cell in step S403.
[0133] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection by the same method as the one used in the case of the
ordinary (conventional) "stand-alone cell."
[0134] On the other hand, when the sequence in the "discovery
signal" is determined as the sequence for the "macro-assisted
cell," the mobile station UE receives the control signals
corresponding to the MIB and the SIB of the small cell in step S404
through the individual control signal, the broadcast information,
and the like from the macro radio base station Macro eNB.
[0135] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection on the basis of the individual control signal from the
macro radio base station Macro eNB.
[0136] According to the mobile communication system of the third
modified example, the mobile station UE can determine whether the
small cell is the "stand-alone cell" or the "macro-assisted cell"
on the basis of the detected sequence in the "discovery
signal."
[0137] As a consequence, a particular small cell can be operated
both as the "stand-alone cell" and as the "macro-assisted cell" by
changing the sequence in the "discovery signal" transmitted in the
small cell.
Fourth Modified Example
[0138] A mobile communication system according to a fourth modified
example of the present invention will be described with reference
to FIG. 12 to FIG. 14, while focusing on differences from the
above-described mobile communication system according to the first
embodiment.
[0139] In the mobile communication system according to the fourth
modified example, the transmission unit 111 in the small radio base
station Small eNB is configured to transmit the MIB through a P-BCH
(physical-broadcast channel) as shown in FIG. 12 and FIG. 13.
[0140] The MIB may include an identifier for notifying whether the
cell transmitting the MIB is the "stand-alone cell" or the
"macro-assisted cell."
[0141] The control unit 22 is configured to determine whether the
small cell is the "stand-alone cell" or the "macro-assisted cell"
on the basis of the content of notification by the MIB.
[0142] Here, when the small cell is determined as the "stand-alone
cell," the control unit 22 is configured to start the communication
in the small cell on the basis of the SIB of the small cell. In
other words, the control unit 22 is configured to establish the
connection (the U-plane and the C-plane) in the "stand-alone
cell."
[0143] On the other hand, when the small cell is determined as the
"macro-assisted cell," the control unit 22 is configured to start
the communication in the small cell on the basis of the control
signal from the macro cell. In other words, the control unit 22 is
configured to establish the connection in the small cell on the
basis of the control (the C-plane) exchanged between the macro
radio base station Macro eNB and the mobile station UE.
[0144] An operation of the mobile station LIE of the fourth
modified example will be described below with reference to FIG.
14.
[0145] As shown in FIG. 14, in step S501, the mobile station UE
receives the MIB after detecting the PSS/SSS in the small cell. In
step S502, the mobile station UE determines whether the small cell
is the "stand-alone cell" or the "macro-assisted cell" on the basis
of the content of notification by the MIB (the identifier included
in the MIB).
[0146] When the small cell is determined as the "stand-alone cell,"
the mobile station UE receives the SIB of the small cell in step
S503.
[0147] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection by the same method as the one used in the case of the
ordinary (conventional) "stand-alone cell."
[0148] On the other hand, when the small cell is determined as the
"macro-assisted cell," the mobile station UE receives the control
signal corresponding to the SIB of the small cell in step S504
through the individual control signal, the broadcast information,
and the like from the macro radio base station Macro eNB.
[0149] In this case, if the mobile station UE establishes the
connection to the small cell, the mobile station UE establishes the
connection on the basis of the individual control signal from the
macro radio base station Macro eNB.
[0150] The individual control signal may be notified by use of the
RRC layer, or any other layers including the PDCP layer, the RLC
layer, the MAC layer, the physical layer, and the like.
[0151] According to the mobile communication system of the fourth
modified example, the mobile station UE can determine whether the
small cell is the "stand-alone cell" or the "macro-assisted cell"
on the basis of the MIB received from the small radio base station
Small eNB.
[0152] As a consequence, a particular small cell can be operated
both as the "stand-alone cell" and as the "macro-assisted cell" by
changing the content of notification by (the identifier in) the MIB
transmitted in the small cell.
Fifth Modified Example
[0153] A mobile communication system according to a fifth modified
example of the present invention will be described with reference
to FIG. 15 and FIG. 16, while focusing on differences from the
above-described mobile communication system according to the first
embodiment.
[0154] In the mobile communication system according to the fifth
modified example, as shown in FIG. 15, the transmission unit 31 in
the macro radio base station Macro eNB is configured to use SIB5 to
transmit an information element for notifying whether a cell as a
candidate for cell reselection at a different frequency, which is
the cell notified in the SIB5, is the "stand-alone cell" or the
"macro-assisted cell."
[0155] For example, the information element may notify a fact that
only the "macro-assisted cell" is present on a carrier for the cell
reselection at the different frequency notified in the SIB5 whereas
no "stand-alone cells" are present thereon. In this case, the
information element may notify information concerning the
"macro-assisted cell" (such as information concerning radio
resources of the "discovery signal").
[0156] Alternatively, the information element may notify a fact
that only the "stand-alone cell or cells" are present on the
carrier for the cell reselection at the different frequency
notified in the SIB5.
[0157] Here, the transmission unit 31 may be configured to transmit
any of the information elements by using an individual control
signal such as "measurement configuration."
[0158] The control unit 22 in the mobile station UE is configured
to determine whether or not the SIB5 or the like notifies that the
carrier on which the small cell being a target to undergo cell
reselection processing (the cell reselection) is located is the
carrier on which only the "stand-alone cell or cells" are
present.
[0159] Here, when the control unit 22 determines that the SIB5
notifies that only the "stand-alone cell or cells" are present on
the carrier, the control unit 22 receives the MIB/SIB of the small
cell after detecting the PSS/SSS transmitted in the cell.
[0160] Meanwhile, when the communication is to be started, the
control unit 22 is configured to establish the connection to the
small cell by the same method as the one used in the case of the
ordinary (conventional) "stand-alone cell," and then to start the
communication. In other words, the control unit 22 is configured to
establish the connection (the U-plane and the C-plane) in the
"stand-alone cell."
[0161] On the other hand, when the control unit 22 determines that
the SIB5 `does not notify that only the "stand-alone cell or cells"
are present on the carrier,` i.e., that the SIB5 `notifies that
only the "macro-assisted cell" is present on the carrier,` the
control unit 22 is configured to start the communication in the
small cell on the basis of the individual control signal from the
macro radio base station Macro eNB. In other words, the control
unit 22 is configured to establish the connection in the small cell
on the basis of the control (the C-plane) exchanged between the
macro radio base station Macro eNB and the mobile station UE.
[0162] Meanwhile, the control unit 22 is configured to perform the
cell reselection processing and measurement processing on the
carrier on the basis of the above-described information element
notified by way of the SIB5.
[0163] Alternatively, the control unit 22 may be configured to
determine that the small cell is the "stand-alone cell" if the
macro cell is not present.
[0164] In the above-described example, the SIB5 notifies the fact
that `only the "macro-assisted cell" is present on the carrier for
the cell reselection at the different frequency` or the fact that
`only the "stand-alone cell or cells" are present thereon.`
Instead, the SIB5 may notify a fact that "the "macro-assisted cell"
as well as the "stand-alone cell or cells" are present on the
carrier for the cell reselection at the different frequency."
[0165] In this case, the mobile station UE may perform both of the
processing to detect the "stand-alone cell" by using the PSS/SSS
and the processing to detect the "macro-assisted cell" on the basis
of the individual control signal from the macro radio base station
Macro eNB.
[0166] An operation of the mobile station UE of the fifth modified
example will be described below with reference to FIG. 16.
[0167] As shown in FIG. 16, in step S601, the mobile station UE
determines whether or not cell selection processing (cell
selection) is to be performed.
[0168] When the mobile station UE determines that the cell
selection processing is to be performed, the mobile station UE
detects the small cell by detecting the PSS/SSS, and then receives
the MIB/SIB in step S604.
[0169] Here, if the mobile station UE establishes the connection to
the small cell, the mobile station UE establishes the connection by
the same method as the one used in the case of the ordinary
(conventional) "stand-alone cell."
[0170] Here, the cell selection processing means an operation by
the mobile station UE to conduct cell search from scratch without
being located in any cell, and hence to detect a particular cell.
The cell selection processing takes place, for example, immediately
after the mobile station UE is turned on or when the mobile station
UE is outside a coverage area of a certain cell.
[0171] In the meantime, once the mobile station UE detects an
accessible cell, the mobile station UE reads the broadcast
information of the cell and enters the coverage area of the cell.
Thereafter, the mobile station UE changes the cell in which to be
located by performing the cell reselection processing along with a
transfer and the like.
[0172] Here, in the cell reselection processing, the mobile station
UE may perform the cell reselection involving a nearby cell that
uses the same frequency or perform the cell reselection involving a
nearby cell that uses a different frequency.
[0173] Specifically, when the mobile station UE determines in step
S601 that "the cell selection processing is not to be performed
(the cell reselection processing is to be performed)," the mobile
station UE proceeds to step S602.
[0174] In the following description, in step S602, the mobile
station UE is assumed to be located in the macro cell in the 2 GHz
band which is shown in FIG. 1.
[0175] Meanwhile, the carrier as the candidate for the cell
reselection to be notified in the SIB5 of the macro cell is assumed
to be the carrier at 3.5 GHz shown in FIG. 1. In other words, the
small cells are operated on the carrier as the candidate for the
cell reselection.
[0176] The mobile station UE receives the SIB5 transmitted from the
macro radio base station Macro eNB and acquires information on the
cell or the carrier as the candidate for the cell reselection.
[0177] Here, the mobile station UE determines whether or not the
information notifies that the carrier as the candidate for the cell
reselection is the carrier on which only the "stand-alone cell or
cells" are present, on the basis of the information.
[0178] When the mobile station UE determines that the carrier as
the candidate for the cell reselection is notified as the carrier
on which only the "stand-alone cell or cells" are present, the
mobile station UE detects the PSS/SSS and then receives the MIB/SIB
in step S604.
[0179] Here, if the mobile station UE establishes the connection to
the small cell, the mobile station UE establishes the connection by
the same method as the one used in the case of the ordinary
(conventional) "stand-alone cell."
[0180] On the other hand, when the mobile station UE determines
that the carrier as the candidate for the cell reselection is not
notified as the carrier on which only the "stand-alone cell or
cells" are present, the mobile station UE receives the control
signals corresponding to the MIB/SIB of the small cell on the
carrier in step S603 through the individual control signal, the
broadcast information, and the like from the macro cell.
[0181] Here, if the mobile station UE establishes the connection to
the small cell, the mobile station UE establishes the connection on
the basis of the individual control signal from the macro radio
base station Macro eNB.
[0182] According to the mobile communication system of the fifth
modified example, the mobile station UE can determine whether the
cell on the carrier, on which the small cell is deployed, is the
"stand-alone cell" or the "macro-assisted cell" on the basis of the
SIB5 transmitted from the macro radio base station Macro eNB.
[0183] As a consequence, a particular small cell can be operated
both as the "stand-alone cell" and as the "macro-assisted cell" by
changing the content of notification by (the information element
in) the SIB5 transmitted by the macro radio base station Macro
eNB.
[0184] In the above example, the macro cell provided by the macro
radio base station Macro eNB and the "stand-alone cell" provided by
the small radio base station Small eNB have been described as if
they were of different types. Instead, the macro cell provided by
the macro radio base station Macro eNB may be the cell of the same
type as the "stand-alone cell" provided by the small radio base
station Small eNB.
[0185] In the latter case, the cell can be operated as the macro
cell as described above, and can also be operated as the small cell
serving as the "stand-alone cell."
Sixth Modified Example
[0186] A mobile communication system according to a sixth modified
example of the present invention will be described with reference
to FIG. 17, while focusing on differences from the above-described
mobile communication system according to the first embodiment.
[0187] In the mobile communication system according to the sixth
modified example, the small radio base station Small eNB switches
the small cell so as to be operated either as the "stand-alone
cell" or as the "macro-assisted cell" depending on an operation
status of the macro cell under control of the macro radio base
station Macro eNB.
[0188] An operation of the small radio base station Small eNB of
the sixth modified example will be described below with reference
to FIG. 17.
[0189] As shown in FIG. 17, in step S701, the small radio base
station Small eNB determines whether or not the macro cell under
control of the macro radio base station Macro eNB is in an operable
state.
[0190] When the macro cell under control of the macro radio base
station Macro eNB is determined to be in the operable state, the
small radio base station Small eNB switches the small cell under
its control so as to be operated as the "macro-assisted cell" in
step S702.
[0191] On the other hand, when the macro cell under control of the
macro radio base station Macro eNB is determined to be not in the
operable state, the small radio base station Small eNB switches the
small cell under its control so as to be operated as the
"stand-alone cell" in step S703.
[0192] The features of this embodiment described above may be
expressed as follows.
[0193] A first feature of the embodiment is summarized as a mobile
station UE used in a mobile communication system provided with a
macro cell and a small cell, where the small cell is any of a
"stand-alone cell (first cell)" capable of being operated
independently of the macro cell and a "macro-assisted cell (second
cell)" incapable of being operated independently of the macro cell,
the mobile station UE including: a reception unit configured to
detect a "discovery signal (prescribed signal)" transmitted by the
small cell; and a control unit 22 configured to determine whether a
sequence in the "discovery signal" is a sequence for the
"stand-alone cell" or a sequence for the "macro-assisted cell."
Here, when the sequence in the "discovery signal" is determined as
the sequence for the "stand-alone cell", the control unit 22 is
configured to start communication in the small cell on the basis of
MIB/SIB (broadcast information) of the small cell, and when the
sequence in the "discovery signal" is determined as the sequence
for the "macro-assisted cell", the control unit 22 is configured to
start the communication in the small cell on the basis of a control
signal from the macro cell.
[0194] A second feature of the embodiment is summarized as a mobile
station UE used in a mobile communication system provided with a
macro cell and a small cell, where the small cell is any of a
"stand-alone cell" capable of being operated independently of the
macro cell and a "macro-assisted cell" incapable of being operated
independently of the macro cell, the mobile station UE including: a
reception unit 21 configured to detect a PSS/SSS (synchronization
signal) transmitted by the small cell; and a control unit 22
configured to determine whether a sequence in the PSS/SSS is a
sequence for the "stand-alone cell" or a sequence for the
"macro-assisted cell." Here, when the sequence in the PSS/SSS is
determined as the sequence for the "stand-alone cell", the control
unit 22 is configured to start communication in the small cell on
the basis of MIB/SIB of the small cell, and when the sequence in
the PSS/SSS is determined as the sequence for the "macro-assisted
cell", the control unit 22 is configured to start the communication
in the small cell on the basis of a control signal from the macro
cell.
[0195] A third feature of the embodiment is summarized as a mobile
station UE used in a mobile communication system provided with a
macro cell and a small cell, where the small cell is any of a
"stand-alone cell" capable of being operated independently of the
macro cell and a "macro-assisted cell" incapable of being operated
independently of the macro cell, the mobile station UE including: a
reception unit 21 configured to detect a PSS/SSS transmitted by the
small cell, and then to receive a new signal (prescribed signal)
transmitted by using a subframe which is the same as or located at
the periphery of a subframe of the PSS/SSS; and a control unit 22
configured to determine whether the small cell is the "stand-alone
cell" or the "macro-assisted cell" on the basis of a content of
notification by the new signal. Here, when the small cell is
determined as the "stand-alone cell", the control unit 22 is
configured to start communication in the small cell on the basis of
MIB/SIB of the small cell, and when the small cell is determined as
the "macro-assisted cell", the control unit 22 is configured to
start the communication in the small cell on the basis of a control
signal from the macro cell.
[0196] A fourth feature of the embodiment is summarized as a mobile
station UE used in a mobile communication system provided with a
macro cell and a small cell, where the small cell is any of a
"stand-alone cell" capable of being operated independently of the
macro cell and a "macro-assisted cell" incapable of being operated
independently of the macro cell, the mobile station UE including: a
reception unit 21 configured to detect a PSS/SSS transmitted by the
small cell, and then to receive a "discovery signal (prescribed
signal)"; and a control unit 22 configured to determine whether a
sequence in the "discovery signal" is a sequence for the
"stand-alone cell" or a sequence for the "macro-assisted cell."
Here, when the sequence in the "discovery signal" is determined as
the sequence for the "stand-alone cell", the control unit 22 is
configured to start communication in the small cell on the basis of
MIB/SIB of the small cell, and when the sequence in the "discovery
signal" is determined as the sequence for the "macro-assisted
cell", the control unit 22 is configured to start the communication
in the small cell on the basis of a control signal from the macro
cell.
[0197] A fifth feature of the embodiment is summarized as a mobile
station UE used in a mobile communication system provided with a
macro cell and a small cell, where the small cell is any of a
"stand-alone cell" capable of being operated independently of the
macro cell and a "macro-assisted cell" incapable of being operated
independently of the macro cell, the mobile station UE including: a
reception unit 21 configured to receive MIB (broadcast information)
transmitted by the small cell; and a control unit 22 configured to
determine whether the small cell is the "stand-alone cell" or the
"macro-assisted cell" on the basis of a content of notification by
the MIB. Here, when the small cell is determined as the
"stand-alone cell", the control unit 22 is configured to start
communication in the small cell on the basis of SIB (rest of the
broadcast information) of the small cell, and when the small cell
is determined as the "macro-assisted cell", the control unit 22 is
configured to start the communication in the small cell on the
basis of a control signal from the macro cell.
[0198] A sixth feature of the embodiment is summarized as a mobile
station UE used in a mobile communication system provided with a
macro cell and a small cell, where the small cell is any of a
"stand-alone cell" capable of being operated independently of the
macro cell and a "macro-assisted cell" incapable of being operated
independently of the macro cell, the mobile station UE including: a
control unit 22 configured to determine whether or not SIB5
(specific broadcast information) of the macro cell notifies that a
carrier for cell reselection is a carrier on which only the
"stand-alone cell" is present. Here, when the control unit 22
determines that SIB5 notifies that the carrier for the cell
reselection is the carrier on which only the "stand-alone cell" is
present, the control unit 22 is configured to perform the cell
reselection of the cell on the carrier, and then to start
communication in the cell on the basis of MIB/SIB (broadcast
information) of the cell, and when the control unit 22 determines
that SIB5 does not notify that the carrier for the cell reselection
is the carrier on which only the "stand-alone cell" is present, the
control unit 22 is configured to start the communication with the
cell on the carrier on the basis of a control signal from the macro
cell.
[0199] A seventh feature of the embodiment is summarized as a small
radio base station Small eNB configured to manage a small cell,
where the small cell under control of the small radio base station
Small eNB is any of a "stand-alone cell" capable of being operated
independently of a macro cell under control of a macro radio base
station Macro eNB and a "macro-assisted cell" incapable of being
operated independently of the macro cell, the small radio base
station Small eNB including: a transmission unit 11 configured to
transmit a "discovery signal (prescribed signal)". Here, the
transmission unit 11 is configured to use a sequence for the
"stand-alone cell" as a sequence in the "discovery signal" when the
small cell under control of the small radio base station Small eNB
is operated as the "stand-alone cell", and to use a sequence for
the "macro-assisted cell" as the sequence in the "discovery signal"
when the small cell under control of the small radio base station
Small eNB is operated as the "macro-assisted cell".
[0200] Here, the determination as to whether the above-described
small cell is operated by using the "macro-assisted cell" or the
"stand-alone cell" may be made by the small radio base station
Small eNB alone, by the macro radio base station Macro eNB alone,
or in cooperation with each other, and on the basis of statuses of
the nearby cells (operating statuses of the radio base stations
eNB, the degree of congestion of the cells, the number of the
located or connected mobile stations UE, and so forth). Hence, the
switching between the "macro-assisted cell" and the "stand-alone
cell" may be performed automatically.
[0201] Meanwhile, when the small cell is switched from the
"stand-alone cell" to the "macro-assisted cell," the mobile station
UE having been connected to the small cell may be subjected to
release processing from the small cell (a handover to another cell,
transition to another RAT, restriction control, or IDLE
transition).
[0202] Moreover, a request regarding the switching between the
"macro-assisted cell" and the "stand-alone cell" may be received
from a core network or a mobile station.
[0203] A eighth feature of the embodiment is summarized as a
communication control method for a mobile station UE usable in a
mobile communication system provided with a macro cell and a small
cell, where the small cell is any of a "stand-alone cell" capable
of being operated independently of the macro cell and a
"macro-assisted cell" incapable of being operated independently of
the macro cell, the method including: a first step of detecting a
"discovery signal (prescribed signal)" transmitted by the small
cell; a second step of determining whether a sequence in the
"discovery signal" is a sequence for the "stand-alone cell" or a
sequence for the "macro-assisted cell"; and a third step of
starting communication in the small cell. Here, when the sequence
in the "discovery signal" is determined as the sequence for the
"stand-alone cell" in the second step, the communication in the
small cell is started in the third step on the basis of MIB/SIB
(broadcast information) of the small cell, and when the sequence in
the "discovery signal" is determined as the sequence for the
"macro-assisted cell" in the second step, the communication in the
small cell is started in the third step on the basis of a control
signal from the macro cell.
[0204] A ninth feature of the embodiment is summarized as a small
radio base station Small eNB configured to manage a small cell,
where the small cell is any of a "stand-alone cell" capable of
being operated independently of a macro cell under control of a
macro radio base station Macro eNB and a "macro-assisted cell"
incapable of being operated independently of the macro cell. Here,
the small radio base station switches the small cell so as to be
operated as any one of the "stand-alone cell" and the
"macro-assisted cell" depending on an operation status of the macro
cell.
[0205] It should be noted that the foregoing operations of the
mobile station UE and the radio base station eNB may be implemented
by hardware, may be implemented by a software module executed by a
processor, or may be implemented in combination of the two.
[0206] The software module may be provided in a storage medium in
any format, such as a RAM (Random Access Memory), a flash memory, a
ROM (Read Only Memory), an EPROM (Erasable Programmable ROM), an
EEPROM (Electronically Erasable and Programmable ROM), a register,
a hard disk, a removable disk, or a CD-ROM.
[0207] The storage medium is connected to a processor so that the
processor can read and write information from and to the storage
medium. Instead, the storage medium may be integrated in a
processor. The storage medium and the processor may be provided
inside an ASIC. Such an ASIC may be provided in the mobile station
UE and the radio base station eNB. Otherwise, the storage medium
and the processor may be provided as discrete components inside the
mobile station UE and the radio base station eNB.
[0208] Hereinabove, the present invention has been described in
detail by use of the foregoing embodiments. However, it is apparent
to those skilled in the art that the present invention should not
be limited to the embodiments described in the specification. The
present invention can be implemented as an altered or modified
embodiment without departing from the spirit and scope of the
present invention, which are determined by the description of the
scope of claims. Therefore, the description of the specification is
intended for illustrative explanation only and does not impose any
limited interpretation on the present invention.
[0209] Note that the entire content of Japanese Patent Application
No. 2012-167507 (filed on Jul. 27, 2012) is incorporated by
reference in the present specification.
INDUSTRIAL APPLICABILITY
[0210] As described above, according to the present invention, it
is possible to provide a mobile station, a small radio base
station, and a communication control method, which are capable of
realizing a "macro-assisted cell" adaptable to multiple operation
modes.
EXPLANATION OF THE REFERENCE NUMERALS
[0211] Macro eNB macro radio base station [0212] Small eNB small
radio base station [0213] UE mobile station [0214] 111, 23, 31
transmission unit [0215] 112, 21, 32 reception unit [0216] 22
control unit
* * * * *
References